Hydrophilic polyurethane foam structure and process



United States Patent HYDROPHILIC POLYURETHANE FOAM STRUCTURE AND PROCESS No Drawing. Application November 21, 1957 Serial No. 697,778

- 3 Claims. (Cl. 117-98) This invention relates to improvements in porous structures, and more particularly to a process for improving thewater absorption capacity of polyurethane foams and to the improved products of the process.

,Bolyurethane foams form sponge-like materials having abrasive, wear-resistant, heat-resistant surfaces. Polyurethane foams, however, unlike regenerated cellulose and natural sponges, are strongly hydrophobic and thus'do not absorb water except by a slight wicking action. Likewise, the permeability of polyurethane foams is very low since a portion of the closed pores caused by foam bubblesdoj not break, or do not break on all faces, during the foaming and curing steps. Thin skins appear to stretch between all the lamellae of the cured foams preventing freeflow.

of fluids through the foam.

Itis obvious that if hydrophobic polyurethane foams could be made hydrophilic, i.e., could be made to more readily absorb water, the flushing of dirt from the foams would be facilitated, there would be less physical effort required to squeeze or wring fluid from the foam, the foams would pick up more fluid when squeezed and released under the surface of the fluid, the foams could absorb more fluid in a given time, and in general the utility of these foams would be greatly enhanced. However, the expedients heretofore suggested for rendering polyurethane foams hydrophilic have failed to produce a satisfactory improvement in fluid absorption, or have deteriorated the foam to such a degree that the foam for any pratical purpose was rendered useless.

Anobject of this invention, therefore, is to provide a simple, economical process for rendering polyurethane foam structures hydrophilic. Another object is to provide modified polyurethane foam structures which are hydrophilic, i.e., which more rapidly absorb greater quantities of water than do unmodified polyurethane foam structures. The foregoing and other objectives will more clearly appearhereinafter.

These objects are realized by the present invention which, briefly stated, comprises impregnating a porous structure of a polyurethane foam with an aqueous solu tion of aluminum sulfate and thereafter drying the impregnated structure at elevated temperatures whereby to produce a hydrophilic porous structure of polyurethane foam, the pore walls of which are coated with aluminum sulfate.

7, The preparation of polyurethane. foam structures by reacting water with free isocyanate radical-containing organic polymeric products is described in "German Plastics Practice by De Bell et al., 1946, pp. 316 and 463- 465. Polyurethane foams applicable to this invention may be produced by employing reactants and'methods, such as disclosed in US. Patents Numbers 2,282,827 (Rothrock); 2,284,637 (Catlin); 2,284,896 (Hanford et al.); 2,292,443 (Hanford); 2,333,639 (Christ et al.); 2,358,475 (Pratt et al.); 2,374,163 (Rothrock); 2,787,601

, (Detrick et al.); and U8. applications Serial Numbers 369,240 now Patent No. 2,788,335 (Barthel), filed July 20, 1953; 383,370, now-Patent No. 2,833,730 (Barthel), filed September 30, 1953; 395,843, now Patent No. 2,842,506 (Roussel), filed December 2, 1953; and 405,036, now Patent No. 2,814,600 (Mitchell), filed January 9, 1954. In general, the free isocyanate radicalcontaining organic polymers embrace a wide variety of compounds and are prepared by reacting a polymeric organic substance containing a plurality of groups containing active hydrogen atoms with an organic compound containing as the sole reacting group a plurality of isocyanate groups. 1

An organic compound containing as the sole reacting group a plurality of isocyanate groups may be any of 1 the poly-NCO compounds, i.e., any polyisocyanate. The

-diethanolamine, N-ethylethanolamine, triethanolamine,

preferred compounds are those having two groups of the formula -NCO. Examples of this class are: 2,4-toluene diisocyanate, 2,6-toluene .diisocyanate, m-phenylene diisocyanate, 4-chlorol,3-phenylene diisocyanate, 1-

. chloro-phenylene -2,4-toluene diisocyanate and naphthalene-1,5-diisocyanate.

Polymeric organic substances containing a plurality of groups containing active hydrogen may be selected from a wide variety of polyfunctional compounds, including polyamines, polyalcohols, aminoalcohols, polyhydroxy ethers, polyhydroxy esters, polyamides, polythiols, polysulfonamidesand various mixtures of these types. Typical of manyorganic'compounds which are useful in this connection are ethylene glycol, diethylene glycol, glycerine,

adipamide, m-phenylene diamine, propylene diamine, sulfanilamide, p-aminophenol, succinamide and 2,4-toluene diar'nine. Other long chain polyhydroxy and polycarboxy compounds useful in this invention are alkyd resins containing terminal hydroxyl and carboxyl groups. Examples of the alkyd resinreactants are: glycols, glycerine, trimethylol propane reacted with dibasic acids, such as adipic, phthalic, succinic, maleic and carbonic. The term active hydrogen is used herein to denote.

hydrogen atoms which display activity according to the.

Zerewitinoif tests, as described by Kohler in Journal of American Chemical Society, 49, p. 3181 (1927).

A tertiary amine catalyst is preferably used during the formation of the foam to accelerate the reaction between the isocyanate, water and active hydrogen-containing compounds, and also by proper selection of the catalyst to control the rate of foaming and the cell structure of the foam. The catalyst may be omitted and a. longer time for curing may be used, or the reaction may be speeded up by the use of elevated temperatures. However, it is much simpler and more practical to add the tertiary amine catalyst to cause the reaction to take effective as catalysts, and those of relatively low volatility in aqueous solution of aluminum sulfate may vary within the range of from 0.5% to 48%, and preferably from 2% to 4% by weight, based on the total weight of the solution. impregnation of the foam structure by the solution of aluminum sulfate is followed by drying, preferably in air, at an elevated temperature within the range of 50- 120 C.

The following examples of preferred embodiments will further serve to illustrate the principles and practice of this invention. Percentages are by weight unless otherwise indicated.

Example 1 A polyurethane foam was made by mixing 432 grams of a mixture consisting of 80% toluene-2,4-diisocyanate and 20% toluene-2,6-diisocyanate for 10 seconds using bent wire mixers turning at a slow speed with a mixture consisting of Polyester resin grams 1049 Emulsifier (polyoxyethylated vegetable oil) grams" 15 Water cc-.. 38 N-methyl morpholine cc 15 Diatomaceo'us silicaaverage particle size 2.4

microns grams.. 30

1 Polyester resin-reaction product of dlethylene glycol, adipic acid, and trimethyl propane in a 13/13/lm0lar ratio. Physical propertles are:

Viscosity cps..- 16,000 Acid N0. 2.02 Specific gravity 1.194 Percent water 0.17 Solids percent 100 Hydroxyl No. 66.8

As quickly as possible the foam was poured into a mold 13 x 15" x 19". Foaming takes place in about 1 5-30 seconds and is complete in 2 minutes. The foam was cured overnight at room temperature.

The resulting hydrophobic polyurethane foam was impregnated with a 2% solution of aluminum sulfate (AI (SO .H O), squeezed to remove excesssolution and then oven-dried at 70 C. for one hour to produce hydrophilic foam.

The rate of water absorption of the treated foam in any direction was %-1 inch per second in any direction. The rate of absorption for foam made in an identical manner except that it had not been treated as described, was less than /s inch per second. This rate of absorption was measured after thorough washing with water and wringing in a washing machine wringer. The rate was observed by immersing the foam in a water solution at room temperature containing a small amount of nigrosine black water soluble dye and observing the rise of water containing dye.

The improved rate of absorption is further demonstrated by the amount of water picked up from a shallow tray of water in a short time. The sample of the produce described above, 3" x 3" x 1", was thoroughly wet with water and squeezed in a washing machine wringer to remove excess water and weight. The sample was then laid on a porous grid positioned /a." beneath the surface. of the water and after exactly seconds, the sample was removed and weighed to determine. the amount of water absorbed in the foam. A control of the same. sizewas tested in the same manner. The treated foam absorbed 36 grams of water in the allotted time whereas the control sample absorbed only 2 grams of water.

The water permeability of the product of this example was greatly improved over the control. A 1" section of this product was held tightly between 2" pipe flanges and a 2 head of water was maintained above the sample. The rate of water flow through the sample was measured. Controls of the same thickness, made in an identical manner but with no treatment after foaming and curing were also tested. The rate of flow through the treated foam sample was about 5070 grams per minute, and through the control sample was about 3300 grams per minute.

Example 2 A prepolymer was prepared as follows: 300 grams of a polyether block copolymer containing 90% polypropylene oxide with 10% polyethylene oxide (molecular weight approximately 200) and 27.3 grams of toluene diisocyanate were heated together at 120 C. with stirring under a nitrogen blanket for two hours. An additional 64.2 grams of toluene diisocyanate were slowly added at 120 C. during 30 minutes. The reaction mixture was then quickly cooled to 30 C. To form a foam structure, 50 grams of the resulting prepolymer together with 0.5 gram of polyoxyethylated vegetable oil, 0.5 gram of N-methyl morpholine and 0.5 gram of water were rapidly mixed and then poured in a mold to foam. After the foam had raised to its maximum height, it was placed in an oven at 75 C. to cure for 4 hours. This foam was very soft and springy, but does not wet well with water.

A sample of this foam was then impregnated with a solution of aluminum sulfate as described in Example 1 and was oven-dried. The treated sample showed improved wicking and absorption properties of the order of the previous example.

The unique feature of the present invention is that a previously hydrophobic polyurethane foam is made hydrophilic. This property, in addition to its unaltered prop erties of feel, appearance, wear-resistance, heat-resistance, permanent softness, abrasiveness and freedom from bacterial degradation that give it customer appeal, make polyurethane foam sponges desirable for household and industrial useage. As a result of the treatment of this invention, flushing dirt from the foam is improved, less physical effort is required to squeeze or wring the water from the foam, the foam picks up more water when squeezed under the surface of a fluid, and the treated foams absorb more water from the surface in a given time since the foam is more permeable.

. Specific improved products which can be made by application of the above invention, in addition to all-purpose household and industrial scrubbing and wiping sponges mentioned before, include household and industrial scrubbing and wiping mops and a quick-drying sponge mop which is less susceptible to bacterial degradation. Other sponge uses, such as disclosed in Banigan et al., US. Patents Numbers 2,280,022 and 2,295,823 and Saifert, 2,138,712, may apply to the improved product and provide functional uses and wider utility than any sponge herebefore known. It will be understood that polyurethane foams treated so that they become hydrophilic by the treatment of the present invention may be used for any purpose for which their hydrophilic properties render them suitable.

The hydrophilic properties obtained by treating poly.- urethane foam structures in accordance with the process of this invention may be preserved against the deteriorating action of soaps and detergents and rendered permancut by further treating the foam structures with an aqueous dispersion of an inorganic negative colloid such s polysilicic acid, asdescribed and claimed in the co pending application of John Bugosh, Serial No. 734,410,

filed May 12, 1958, or with an aqueous dispersion of finely divided hydrophilic organic polymer, as described and claimed in the copending application of John Bugosh, Serial No. 734,409, filed May 12, 1958.

I claim:

1. A hydrophilic structure comprising a porous structure of a polyurethane foam the pore walls of which are coated with aluminum sulfate.

2. The process which comprises impregnating a polyurethane foam structure with an aqueous solution of 10 aluminum sulfate and thereafter drying said structure.

3. The process which comprises impregnating a poly- References Cited the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2 920383 January 12 1960 John Bugosh It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected belowo 7 Column l line 58, for "of polyurethane" read of a polyurethane column 2 line 10,, after "1953;" insert 381,745, now Patent Noo 2 850 44 (Mitchell) 9 filed September 21, 1953; column 3 line 68 for "produce" read product column l line 19 for "200 read 2000 Signed and sealed this 5th day of July 1960,

(SEAL) Attest:

' KARL H. AXLINE ROBERT c. WATSON Attesting- Officer Corrmissioner of Patents 

3. THE PROCESS WHICH COMPRISES IMPREGNATING A POLYURETHANE FOAM STRUCTURE WITH AN AQUEOUS SOLUTION OF ALUMINUM SULFATE, SAID SOLUTION CONTAINING FROM 2% TO AND 4% OF ALUMINUM SULFATE, AND THEREAFTER DRYING SAID STRUCTURE AT A TEMPERATURE OF FROM 50*-120* C. 